The studies concerning the correlation of regional blood volume (rCBV) to arterial CO2 tension, cerebral blood flow (CBF), changes in systemic blood pressure, and changes in intracranial pressure to assess the explicit role of cerebral blood volume in the control and regulation of cerebral hemodynamics have been completed. These studies were carried out in vivo in rhesus monkeys by applying the method of stimulated x-ray fluroescence to the measure of CBV. The present studies consist of determining the involvement of cerebral blood volume in selected cerebral pathology in patients. At this time these studies are directed at patients with pseudotumor and dementia. Studies on metrazole-induced seizures in rhesus monkeys are being carried out to delineate the separate effect of systemic pressure and tissue metabolic acidoses of changes in CBV and CBF regulation during seizure. A dual semiconductor x-ray detector system with routed inputs to separate memory sections of a multichannel analyzer has been completed to shorten the measurement times. The study of tantalum as a high atomic number tracer has been carried out, but does not appear to be very promising for human applications due to required doses of radiation and tantalum.